I personally think of Google as more of a webmasters friend than Yahoo. I may be proved wrong and do hope Yahoo proves me wrong. I just don't always like the sound of Yahoo's press statements. For example they stated they didn't like affiliate spam sites or something similar. But today they buy in some webmasters opinion the biggest affiliate spammers of them all in Kelkoo.
I personally don't mind Kelkoo or well thought out affiliate sites, but I am unsure to Yahoo's stance. Their UK shopping section is pure affiliate content. It just seems like Yahoo like to earn from affiliate marketing, but want to block anyone else from doing it.
This current policy is one thats makes me worry what Yahoo may roll out in the future if they get Google's market share.